In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, the introduction of Device to Device (D2D) communication is discussed as a new function after Release 12 (see Non Patent Literature 1).
In the D2D communication, a plurality of adjacent user terminals perform direct device-to-device communication without passing through a network. On the other hand, in cellular communication which is normal communication in a mobile communication system, a user terminal performs communication that passes through a network.
It is noted that cases are assumed where assignment of a radio resource used for the D2D communication is led by a network device such as a base station and the assignment thereof is led by a user terminal that performs the D2D communication. When the user terminal itself that performs the D2D communication performs the assignment of the radio resource, it is possible to perform the D2D communication even when a network situation is instable because a disaster such as an earthquake occurs, for example.